How do I choose which zones I will need?

Zones 1-3 allow you to travel within the city of Paris, i.e. within the limits marked in yellow on the map.
With zones 4-5, you can travel throughout the Greater Paris region, and venture even further, to Disneyland Paris, for example, or to Versailles and its chateau, as well as to the Paris airports. (Unlike the Paris Visite card, most other travel passes do not include airport transport.)